The purpose of this study is to evaluate the efficacy of immunotherapy in asthma due to ragweed allergy. Case selection. The study population will consist of at least fifty patients with late summer asthma who have positive skin tests to ragweed but negative skin tests to Alternaria and other molds and to house dust mite and who are not exposed to other antigens such as cat to which they might have allergy. Study design. During the first year all patients will receive immunotherapy with a placebo preparation, a colored buffered solution of histamine. Any subject who does not show a correlation of changes in symptom score and peak expiratory flow rates with ragweed pollen counts and immunochemical measurements of airborne ragweed allergen will be dropped from the study. After the first year subjects will be stratified for skin test reactivity, bronchial reaction to methacholine, and anticipated exposure to ragweed, then assigned to either active or placebo immunotherapy groups. Patients will receive injections of either the colored histamine solution or aqueous ragweed extract. A single lot of lyophilized ragweed antigen will be procured for the entire study and will be used for skin and bronchial challenge testing as well as immunotherapy. This extract will be standardized for allergen content in international units and also for antigen E content. The doses will be individualized according to the patient's reactions, but the total yearly dose of ragweed will be 50-100 micrograms of antigen E. Parameters for evaluating efficacy will include symptom scores, peak expiratory flow rates, bronchial reactivity to antigen and methacholine, and IgE and IgG antibodies to ragweed. Data processing. The data collection, processing, and analysis will be coordinated by the Mayo Department of Medical Statistics and Epidemiology. Investigators. Because patients who meet the strict selection criteria of this protocol are rare, five large midwestern allergy departments will collaborate: the Mayo Clinic in Rochester, MN (coordinating center); the University of Iowa in Iowa City; the University of Michigan in Ann Arbor; the University of Wisconsin in Madison; and the Park-Nicollet Medical Center in Minneapolis. The assays for IgE and IgG antibody to ragweed and the quantitation of airborne ragweed allergen will be performed in the Mayo Allergic Diseases Research Laboratory.